Add umul_ppmm to gmp-arch.hdoc

Add umul_ppmm to gmp-arch.hdoc

To enable “longlong.h” removal, the umul_ppmm is moved to a gmp-arch.h.
The generic implementation now uses a static inline, which provides
better type checking than the GNU extension to cast the asm constraint
(and it works better with clang).

Most of the architecture uses the generic implementation, which is
expanded from a macro, except for alpha, arm, hppa, x86, m68k, mips,
powerpc, and sparc.  The 32 bit architectures the compiler generates
good enough code using uint64_t types, where for 64 bit architecture
the patch leverages the math_u128.h definitions that uses 128-bit
integers when available (all 64 bit architectures on gcc 15).

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>